what % tint is the back windows on a 1999

I dont know, but you could call toyota.

Otherwise if your buying tint to match other windows you can just get it matched at your tinting place or business. They would also be able to tell you the tint darkness.

just got mine done. it's 15% it may look lighter than the back but consider the light coming in through the windsheild makes it look lighter. but trust me it's definetly 15%, i love it wish i did it a year ago.even better at night.